I have a buffalo linkstation that runs linux on it. It's normally a backup system, but you can easily install your own software on it. It comes with perl installed, too. I don't know if it has the modules you may need, though, (such as a serial port library or whatever).

My linkstation is a few years old (an LS-GL v2), so I don't know anything about the current ones. But there are many devices that are similar (KuroBox, ...). If you don't already have a backup device on the network, it would kill two birds with one stone.

These devices often consume little power, and they're not fast servers. But then again, they don't really need to be...

Update: Oh, I forgot to mention: these tend to be pretty small, physically, so they're easy to find a place to put them.